FR2646572A1 - AUTOSYNCHRONOUS ELECTRIC MACHINE WITH CONTROLLED FLOW - Google Patents

Abstract

The invention relates to an electro-mechanical transformer assembly including an electric machine which is able to transform electric energy into mechanical energy, said machine being made up of a stator (1) or armature whose windings are fed with polyphase currents, a rotor (2) which creates an inductor field and includes a winding (5) fed with a variable continuous current (IR), and a sensor (11) for detecting the velocity (n) or position ( theta ), joined to the rotor, in which the inductive field created by the rotor (2) varies according to at least one operating parameter following a command law ( phi IR). Said command law establishes a dependency relation between a current (IR) density setting (CIR) in the rotor and said operating parameter, making it possible to realise a very high torque at low velocity and a lower torque at high velocity, the machine being fed at a continuous low voltage, for example by a common battery.

Description

Self-synchronous 8 flow controlled electric machine
The invention relates to an electric machine capable of transforming electrical energy into mechanical energy, consisting of a stator, or armature, the windings of which are supplied with polyphase currents, a rotor creating an inductive field and a sensor. speed or position coupled to the rotor.

 The problem posed consists in obtaining with a single machine a high speed at low torque and a high torque at low speed, the machine being supplied with a low direct voltage (<100 V). In addition, a precise position control must be achieved.

 The electric machine must make it possible to obtain a precise torque / speed characteristic, essentially turned towards the motorization of mobile machines with on-board energy source.

In other words, this electric machine must be capable
- to move autonomous mobile vehicles of small or medium dimensions on all types of terrain: on flat terrain - where a relatively high speed is required - or on stairs for example or a high torque is required for a low speed;
- perform a positioning function, for example positioning a robot arm.

 The machines concerned are for example wheelchairs for the disabled, handling carts, mobile robots ...

this list is obviously not exhaustive.

 We know machines with direct current and permanent magnets in which the stator is provided with permanent magnets, the rotor rotating in the stator field consists of a wound frame and the direct current (supplied by batteries for example) is brought to the rotor by a set of collecting brushes (forming a so-called mechanical collector). However, these machines pose problems in terms of position control.

 The electromotive force E in these machines is proportional to the rotational speed n of the rotor: E = K n and the torque C is proportional to the intensity I of the current in the machine: C = machine: C = K + II with the same proportionality constant K.

 Another well-known problem exists when there is only a low voltage which appears during a phase of operation in propulsion mode, that is to say when there is a relatively high speed with a low couple. To increase the torque, it would be necessary to increase the intensity of the current, which would produce an unacceptable heating by Joule effect (the machine not being able to dissipate the heat), or a too large bulk and weight. This is the case with forklifts for example, which run flat without problems but cannot tolerate uphill slopes of more than 3%.

Usually, this problem is solved by adding a second engine or a gearbox.

 I1 are cases where such a solution is not suitable, for example when one does not want to increase the weight of the vehicle.

 In addition, the mechanical collector is bulky and is poorly suited to devices of small size and high torque.

 Autosynchronous permanent magnet machines make it possible to avoid some of these drawbacks: they allow precise positioning, avoid the use of collecting brushes, but they also do not offer the torque-speed characteristics suitable for moving mobile vehicles on land. various when the supply voltage is low and when the power source is on board.

Such machines include
- a wound stator supplied with polyphase currents,
- a rotor made up of a permanent magnet,
- sensors of the speed n and of the position e of the rotor, and
- a control system associated with an electronic power converter to obtain the polyphase currents from the direct current supplied by the batteries. The frequency f of these currents imposes the speed of rotation of the rotor, and the intensity IS of the stator current depends on the state of charge of the machine, which corresponds to the torque required to perform the operation.

 The polyphase current setpoints are calculated so as to maintain a constant angle between the stator field and the rotor field (internal angle). Current embodiments make it necessary to maintain these two fields in quadrature in order to recreate an operation of the "DC motor" type.

 In practice, at least one sensor is placed at the level of the machine to measure the speed n and / or the position 8 of the rotor. When only one measurement is made, the other is deduced by calculation. It is however preferable to obtain the two measurements.

 The control system produces CISi setpoints for the intensity of the stator current, the amplitude of which is calculated from the speed error En (difference between the speed setpoint CN and the speed n measured), and the phase of which is calculated so as to maintain the field created by these currents generally in quadrature with the rotor field.

 The CISi instructions (i designating the respective phases of the polyphase currents) are supplied to the electronic power converter which then delivers the polyphase currents corresponding to the stator.

 The object of the invention is an electric machine supplied with direct voltage comprising a rotor supplied with direct current. Typically, the field of induction created by the rotor is variable as a function of at least one operating parameter of the motor and of a control law establishing a dependence relationship between a current intensity setpoint in the rotor and said operating parameter, said law being able to be determined by the operator as a function of the chosen application.

 Advantageously, the operating parameter is a setpoint for the rotational speed of the rotor and / or a measure of the intensity of the stator current.

 It is necessary to associate with the machine thus defined a control system intended to vary the rotor flux by slaving the intensity of the rotor current to the torque / speed characteristic, according to said control law. In addition, an electronic power converter is preferably associated with the control system, in order to produce the rotor current as a function of the current intensity setpoint delivered by the control system.

 Finally, the rotor current intensity setpoint is advantageously developed as a function of at least one of the following parameters: the speed setpoint or the rotor speed, the stator current setpoint or the stator current , the torque setpoint or the torque and the position setpoint or the position of the rotor relative to the stator.

 Other features and advantages of the invention will emerge from the description which follows, with reference to the appended drawings, of nonlimiting exemplary embodiments.

 Figure 1 shows in schematic perspective a machine according to the invention.

 Figure 2 is a cross section through the machine of Figure 1.

 Figure 3 shows, in cross section, the rotor of a machine in an alternative embodiment.

 FIGS. 4A, 4B and 4C schematically represent the control system of a machine according to the invention in three variant embodiments.

 FIGS. 5a to 5e are graphical representations of laws controlling the intensity of the rotor current creating the variable inducing field.

We see in Figures 1 and 2 a machine for ensuring the motorization of a mobile machine. It comprises a stator 1 provided with windings in which polyphase currents pass
IS, the number of these windings being equal to the number i of phases, and a rotor 2 mounted on a shaft 3 and comprising an inductor winding traversed by a direct current IR. In the present example, the rotor comprises a single winding 5 with a pair of batteries and the stator 1 is composed of three windings 1.1, 1.2, 1.3 arranged at 60C and supplied with three-phase current. As shown in Figure 3, the rotor may include a 5 'winding creating several pairs of blades, here two pairs crossed at right angles, the stator (not shown) then being equipped with a three-phase winding with two pairs of blades. pole of the rotor can be provided with a permanent magnet 4 whose magnetic field combines with that created by the winding 5, so that the overall inducing field has a non-zero minimum value in the absence of excitation current in the rotor winding.

 The direct current necessary to supply the machine is supplied for example by a battery mounted on board the mobile machine I1 is brought to the rotor advantageously by known sliding contacts, but any other means of transmitting energy the rotor may be suitable (rotary transformer, optical power link, etc.).

 FIGS. 4A to 4C represent the control system, in three variants, of the assembly 9 composed of the stator 1 and the rotor 2 as described above. The measurement of the rotor current MIR is provided by a sensor 10 and the measurement of the stator current MIS by a sensor 12, while a sensor 11 measures the angular position e or the speed of rotation n of the rotor 2. The polyphase stator current ISi is supplied to stator 1 by an electronic power converter 15 from the measured current MIS and from a current setpoint CISi delivered by a control circuit 13. The DC rotor current IR is supplied to rotor 2 by an electronic power converter 16 from the measured current MIR and from a current setpoint CIR delivered by a control circuit 14. The electronic power converter 15, which is a source of sinusoidal currents 9 cutting using a natural sampling technique, and the converter 16, which uses a device known as a "fork regulator", thus receives the current instructions CISi and CIR from a control assembly 7 composed of the circuits 13 and 14.

The control system processes the information delivered by the sensors according to control laws to supply the electronic power converters with setpoint signals
CIR, CISi indicative of the intensity of the current to be injected into the rotor and the stator, respectively. Electronic power converters supply the desired current to the machine windings.

 More precisely, the information necessary for controlling the current of the stator (6 and n) is obtained from the sensor 11 placed at the level of the rotor to measure at least one of the following mechanical quantities: the position e of the rotor, its speed n , its couple C. The measurement of a single quantity is sufficient, the others can be deduced therefrom by calculation.

 The simplest implementation is to measure e and calculate n and C if necessary.

 The control circuit 13 determines the phase of the polyphase currents of the stator from the signals delivered by the sensor 11 and, possibly, from the sensor 12, this latter arrangement making it possible to vary the internal angle y between the stator and rotor fields (see on this subject the French patent nO 79 15 809). In the latter case, the internal angle is controlled not only by the position of the rotor (conventional autosynchronous machine) but also by the torque and the speed of the machine.

 The control circuit 13 also determines the amplitude of said stator currents from the difference between the speed n of the rotor and the speed reference CN. Finally, it delivers a reference signal CISi comprising the phase and amplitude information necessary for the production by the converter 15 of suitable stator currents ISi.

The control circuit 14 supplies the rotor current setpoint CIR in accordance with one or more predetermined t? IR laws, the setpoint CIR depending on
- the CN speed reference or the rotor speed n,
- the stator intensity setpoint CISi or the stator intensity measured MIS,
- the CC torque or C torque setpoint,
- the deposit. angular position C8 or angular position e of the rotor.

 In the examples shown, the CIR setpoint is a function of the CN speed setpoint (FIG. 4A), of the measured stator current MIS (FIG. 4B) or of these two optional parameters (FIG. 4C), according to a control law t: IR predetermined.

FIGS. 5a to 5e give examples of such control laws, which have the effect of varying the coefficient Kf of proportionality between the speed> n of the rotor and the electromotive force E, by variation of the intensity of the rotor current, in order to honor the various operating points imposed. These laws are chosen essentially according to the technological constraints of which the machine is the object and, consequently, of the chosen application.

 In the case of the laws represented in FIGS. 5a and 5b, the intensity of the direct current injected into the rotor (controlled by the setpoint CIR) is a function of the speed setpoint CN of the rotor. Either to honor, at a given continuous supply voltage U, two operating points M1 and M2 corresponding to respective values n1, C1, P1 and n2, C2, P2 of the speed of rotation n, of the torque C and of the power P. The point M corresponds to a high torque for a low speed and the point M2 has a high speed for a low torque. The corresponding coefficients K1 and K2 can be deduced therefrom by calculation, which makes it possible to impose intensity setpoints in the rotor CIR1 and CIR2 corresponding respectively to said coefficients. The speed setpoints CN1 and CN2 fixing the speeds or the rotor flux must vary are also deduced by the calculation.

In the particular case of FIG. 5b, three operating zones are thus defined
- from O to CN1: the rotor flux is constant, the coefficient K is maximum and the speed control is ensured by the stator current under the control of circuit 13; it is for example a phase of positioning or climbing stairs for the machine, corresponding to a high torque and a low speed;
- from CNl to CN2: the rotor flux and the coefficient vary; piloting is obtained by controlling the rotor current using circuit 14;
- beyond CN2: the rotor flux is constant and the coefficient Kp minimum; the piloting is again ensured by the control of the stator current; it is for example a phase of progression of the machine on flat ground, corresponding to a high speed and a low torque.

 A similar analysis could be made for the control law illustrated in FIG. 5a, with the difference that the variation of the rotor flux is here abrupt at the level of the reference values CN1, CN2, instead of being carried out gradually along a linear segment. of finished slope.

 FIGS. 5c, 5d and 5e show control laws' eIR according to which the rotor current setpoint CIR is a function of the measured current MIS in the stator. The law of FIG. 5c, where the rotor current setpoint CIR varies in proportion to the measured stator current MIS, corresponds to the classic characteristic of a series machine. It is interesting with regard to the propulsion of the machine, but unfavorable relative to the positioning function. The laws of FIGS. 5d and 5e remedy this drawback by creating a horizontal plateau below a value MIS1 and above a value MIS2> MIS1 of the stator current MIS, the lower level corresponds to a high speed regime with low torque and the upper level corresponds to a low speed regime with high torque. In the case of FIG. 5e, the lower bearing is interrupted at a value MIS3 <MIS1 of the stator intensity MIS, below which another bearing is created corresponding to an increased rotor current, which favors a positioning phase at low stator current.

 Those skilled in the art can imagine other control laws t ~ IR, however taking care that they do not lead to an excessive rotor current liable to damage the machine.

 The selected control laws can be obtained by analog and / or digital means.

 It goes without saying that any other instruction or additional law can be introduced into the control system to act on the machine; for example, stop at such time, at such place, etc.

Claims (6)

Claims  1. Electric machine capable of transforming electrical energy into mechanical energy, consisting of a stator (1), or armature, the windings of which are supplied with polyphase currents, a rotor (2) creating an inductive field and d '' a speed (n) or position (6) sensor (11) coupled to the rotor, characterized in that the rotor comprises a winding (5) supplied with variable direct current (IR) so that the inductive field created by the rotor (2) varies as a function of at least one operating parameter of the motor according to a control law (tIR) establishing a dependency relationship between a current intensity set point (CIR) in the rotor and said operating parameter.  2. Electric machine according to claim 1, characterized in that said motor operating parameter is a speed reference (CN) of rotation of the rotor.  3. Electric machine according to claim 1, characterized in that said motor operating parameter is the intensity of the stator current (MIS) measured by a sensor (12) associated with the stator (1).  4. Electric machine according to claim 1, characterized in that said operating parameter is a speed setpoint (CN) and / or the intensity of the stator current (MIS) measured by a sensor (12) associated with the stator (1 ).  5. Electric machine according to one of the preceding claims, characterized in that it comprises a control circuit (14) intended to vary the rotor flux according to said control law tIR), which delivers a setpoint (CIR) å an electronic power converter (16), which produces the rotor current (IR) from said setpoint (CIR).  6. Electric machine according to one of the preceding claims, characterized in that the setpoint (CIR) is produced as a function of at least one of the following parameters - the speed setpoint (CN) or the speed (n) of the rotor  (2), - the stator intensity setpoint (CIS) or  the measured stator intensity (MIS), - the torque setpoint (CC) or the torque (C), and - the position setpoint (cob) or the position (6) of the  rotor (2) relative to the stator (1),